When chemical reactions yield chiral compounds, the separation of enantiomers can be extremely important. In the pharmaceutical industry, for example, oftentimes one enantiomer of a compound provides a beneficial effect while the other enantiomer causes harmful side effects. Thus, “single enantiomer” drugs are often highly desirable.
Unfortunately, it is sometimes difficult to obtain a composition that consists only of one enantiomer of a chiral compound. For example, because of the similarity of the physical properties of the enantiomers, it can be very difficult to isolate a single enantiomer from a racemic mixture.
One method of producing only one enantiomer is called asymmetric synthesis, or chiral synthesis. A strategy that is often attempted in asymmetric synthesis is to use a chiral ligand. The ligand complexes to the starting materials and physically blocks the other trajectory for attack, leaving only the desired trajectory open. This leads to production of only one type of enantiomer of the product.
A class of chiral substances that are typical of the prior art is chiral phosphines, in combination with compounds of rhodium or ruthenium. These complexes work as catalysts for enantioselective synthesis in certain types of reactions, including hydrogenation of functionalized alkenes.
Chiral phosphine ligands and their production and use are described in, for example, U.S. Pat. Nos. 7,078,568 and 6,987,202 to Shimizu et al., U.S. Pat. No. 6,333,291 to Yokozawa et al., U.S. Pat. No. 6,297,387 to Antognazza et al., U.S. Pat. No. 6,172,249 to Berens et al., and U.S. Pat. Nos. 4,397,787 and 4,331,818 to Riley, all of which are hereby incorporated by reference.
These chiral phosphine ligand metal complexes are used for catalysts in the pharmaceutical industry. Catalysts are very important to speed up and sometimes even initiate chemical reactions. As such, there is always a need for cheaper, cleaner, and more stable catalysts that provide high yields. Specifically, in the context of the current invention, there is a need for catalysts that can be used to promote reactions leading to the synthesis of a desired single enantiomer compound.